Structure-function analysis of BfpB, a secretin-like protein encoded by the bundle-forming-pilus operon of enteropathogenic Escherichia coli

Production of type IV bundle-forming pili by enteropathogenic Escherichia c oli (EPEC) requires BfpB, an outer-membrane lipoprotein and member of the s ecretin protein superfamily. BfpB was found to compose a ring-shaped, high- molecular-weight outer-membrane complex that is stable in 4% sodium dodecyl sulfate at temperatures of less than or equal to 65 degreesC. Chemical cro ss-linking and immunoprecipitation experiments disclosed that the BfpB mult imeric complex interacts with BfpG, and mutational studies showed that BfpG is required for the formation and/or stability of the multimer but not for the outer-membrane localization of BfpB. Formation of the BfpB multimer al so does not require BfpA, the repeating subunit of the pilus filament. Func tional studies of the BfpB-BfpG complex revealed that its presence confers vancomycin sensitivity, indicating that it may form an incompletely gated c hannel through the outer membrane. BfpB expression is also associated with accumulation of EPEC proteins in growth medium, suggesting that it may supp ort both pilus biogenesis and protein secretion.